1. Technical Field
The present invention relates to a light scanning device, a method for controlling the light scanning devices and an image display device and, in particular, to a technique for light scanning devices that scan laser light modulated according to image signals.
2. Related Art
Laser-light scanning devices are generally used in image display devices that display images with scanned laser light. The light scanning devices emit laser light modulated in response to image signals in two dimensions. The image display devices display images on screens or the like with laser light scanned from the light scanning devices. An example of the techniques of light scanning devices for displaying images with laser light is disclosed in Patent Document 1: JP-A 2003-207730.
Light scanning devices generate light-source driving signals using pixel timing signals indicative of timings at which laser light enters for every pixel region. The use of the pixel timing signals allows laser light modulated in response to image signals to enter correct positions even if the linear velocity of the laser light changes. However, even when an approximately even amount of laser light is emitted in the case where the linear velocity of the laser light changes, the amount of laser light radiated to a target region shows an uneven distribution. When a light source is driven by an analog system in which the pulse amplitude is controlled in response to image signals, the brightness changes irrespective of the pulse amplitude because of changes in laser-light irradiation time per pixel. For example, when laser light is reciprocated in one dimension of two dimensions, laser-light scanning is slower at both ends and faster in the center, which shows such a distribution of light that it is light at both ends and dark in the center. Also when a light source is driven by a digital system in which the pulse width is controlled in response to image signals, the brightness changes irrespective of the pulse width because of changes in laser-light irradiation time per pixel. Furthermore, the digital system may sometimes cause the problem that the pulse width modulation (hereinafter, referred to as PWM) cannot keep pace with the pixel timing signals. Means for preventing such a problem includes controlling the driving of the light source to changes in the linear velocity of the laser light. In this case, the driving of the light source is controlled on the basis of the linear velocity of the laser light which is determined for each pixel by calculation, which requires complicated control of the light source. As described above, the known technique has the problem of difficulty in emitting light beams with a preferable distribution by simple control.